For anyone who reads this kind of stuff and gets worried (as if we don't have enough real problems to worry about right now), let's be absolutely clear:

1. NATO is not attempting to isolate Kaliningrad and never has been. This is posturing aimed at a non-existent threat.
2. Putin has been throwing around nuclear threats for years now, along with all kinds of other threats of escalation, because he knows they rapidly get traction in Western media. None of his "red lines" have ever amounted to anything yet, and none of them ever will, because...
3. Putin's only goal is his own survival, and there is absolutely no version of starting a war with NATO - especially a nuclear war - that he personally survives. Russia fires one nuke, Moscow gets deleted. It's a matter of dispersion. NATO is an alliance, there's no one single command center. But there's only one Russia. At a fundamental level there is genuinely zero chance that he will follow through on this threat.

This doesn't mean that Russia isn't a threat. Here's what they're actually going to do; they're going to try to break up NATO. If Putin can do that, he's no longer facing an alliance, he's facing a weakened collection of European states that can individually be bullied into submission. Smaller countries like the Baltics can be absorbed, more powerful nations like Germany can be forced out of or into Russia's sphere of influence as fits Putin's purposes.

This threat you're reading about here? It's a part of that plan. Russia announces that they're being "forced" to escalate in response to completely imagined provocations by NATO. Meanwhile their troll farms spread "NATO is Western Imperialism" and "NATO are just leeching off of us" propaganda online (the former for the left, the latter for the right). Credulous westerners hear that NATO is provoking Russia into nuclear war and think "Oh my God why are we even in this alliance?"

That's the game he's playing. And it's going to get worse. There are going to be more direct provocations, from Russia, aimed at testing just how committed the alliance is to defending it's weakest members. He'll try to separate the little guys from the herd and pick them off, while eroding the major players trust in each other.

That's the real danger. Not that Putin is going to go nuclear over a threat to Kaliningrad that he made up.